1. Field of the Invention
The present invention pertains to circuitry for sorting fruit according to the color thereof, and more particularly, it pertains to circuitry for sorting fruit being transported upon a plurality of conveyor paths by separately measuring and comparing the light reflected from the surface of each fruit within two different bands of wavelengths of light.
2. Description of the Prior Art
Colorimetry, i.e., the analysis of objects upon the basis of their color is used in the variety of fruit and vegetable sorting applications. Color sorting circuitry which has been specifically designed for the sorting of fruits or vegetables generally provides some means for measuring the reflectance properties of the fruit or vegetable being tested. The reflectance of a surface is a measure of the percentage of incident light reflected by it, and colored objects have different reflectances for light of different wavelengths. The relationship between reflectance and the illuminating wavelength for a fruit being tested will produce a characteristic curve which can then be used in the design of apparatus and circuitry for color rating that fruit. That is to say, a fruit may be classified as to color by suitably measuring, describing, and classifying its reflectance curve, and fruit may be sorted into different grades by denoting the differences between the reflectance curves for the various grades and testing for these differences.
Some of the prior art systems for measuring the characteristics of fruit or the like include circuitry which measures the reflectance of the fruit in two different bands of wavelengths of light. One of the selected bands will include a wavelength wherein the variation of reflectance between distinct color grades is at a maximum, and the other band may comprise wavelengths wherein there is little or no variation in reflectance between the different grades of fruit. The determination of the color of the fruit can then be measured by observing the difference in the value of the reflectance at the two different bands of wavelengths. In typical prior art systems photodetectors are utilized for converting reflected light in two distinct bands into a pair of electrical signals which are indicative of the amount of light reflected by the fruit within these two different wavelength bands. In one particular prior art system these light reflection signals are amplified and then continuously electronically divided to provide an analog ratio signal which is proportional to the ratio of the light reflection signals which, in turn, corresponds to the relative amount of the characteristic color in the fruit. Voltage comparators are provided for comparing this ratio signal with a plurality of fixed ratio signals representative of the cut points between adjacent color grades, and logic circuitry is connected with such comparators to interrogate the various comparisons so as to obtain a discharge signal in order to direct the fruit being viewed to a particular discharge location in accordance with its determined color grade. Such circuitry is required for each of the conveyors or conveyor paths in the apparatus which carries fruit to the areas where the sorting occurs, and such circuitry is shown in the prior United States patent to Irving et al U.S. Pat. No. 3,750,883. Other prior art color sorting systems use various circuits for directly comparing the two electrical signals from the photodetectors to determine whether or not they exceed a fixed ratio signal or a series of fixed ratio signals.
The aforedescribed circuitry, including the circuitry shown in the aforementioned Irving et al patent, includes amplifiers and ratio circuits, however, which are relatively expensive so that the systems become relatively expensive for a conventional fruit sorting operation where a plurality of conveyors or separate conveyor paths are used.